Nanoimprinting technique is a technique comprising pressing a mold having a pattern of depressions and protrusions formed thereon against a liquid resin or the like on a substrate to transfer the pattern of the mold onto the resin. As such patterns of depressions and protrusions, those from nanoscale of 10 nm-level to about 100 μm are present, and they have been used in various fields, such as fields of semiconductor materials, optical materials, memory media, micro machines, biotechnology and environment.
The type of nanoimprinting is, for example, thermal nanoimprinting comprising bringing a mold, on a surface of which a given shape has been provided, into pressure contact with a thermoplastic resin melted at a temperature of not lower than the glass transition temperature to thermally nanoimprint the surface shape of the mold onto the thermoplastic resin, cooling the mold and then removing the mold, or photo nanoimprinting comprising pressing a mold similar to the above mold against a photo-curable resin, curing the photo-curable resin by irradiation with energy rays such as ultraviolet rays and then removing the mold.
On the other hand, taking strength, hardness, processability, dimensional stability, etc. into consideration, quartz, silicon or the like is usually used for the mold. These materials, however, have problems that they are liable to be broken, are expensive and need a long time for producing a mold, and in order to solve these problems, a replica mold is produced using the mold of quartz or the like as a master mold to thereby cope with the mass production.
As the replica mold, a mold made of a resin is known from the viewpoints of general-purpose properties and cost. This is a resin mold for nanoimprinting.
Such a resin mold for nanoimprinting is formed by bringing a master mold into contact with a laminate consisting of a substrate and a resin layer to transfer a depression-protrusion shape having been formed on the master mold to the resin layer of the laminate. The nanoimprinting is a method in which a laminate consisting of a substrate and a resin such as PMMA laminated on the substrate is brought into contact with the thus formed resin mold for nanoimprinting under heating at a temperature of not lower than the glass transition temperature (Tg) to transfer the depressions and protrusions having been formed on the resin mold for nanoimprinting onto the resin 5. After the transfer is carried out as above, the resin is cooled, and then the resin is released from the resin mold for nanoimprinting, whereby the depression-protrusion shape having been formed on the mold can be transferred to the resin 5. This is an example of thermal transfer, and in addition to such thermal transfer, photo-curing transfer using a photo-curable resin as the resin has been carried out to transfer the depression-protrusion shape.
By bringing the resin mold for nanoimprinting formed as above into contact with a thermoplastic resin or a photo-curable resin or a film on which such a resin has been laminated and transferring the depression-protrusion shape having been formed on the resin mold surface to the surface of the thermoplastic resin or the photo-curable resin, various devices can be produced.
However, the replica mold used as above and the thermoplastic resin or the photo-curable resin to which the depression-protrusion shape is to be transferred are both resins, and therefore, when the resin is released, the depression-protrusion shape having been formed on the replica mold is sometimes broken off, or also the depression-protrusion shape transferred to the thermoplastic resin or the photo-curable resin is sometimes broken off.
On this account, a film of an oxide such as silicon oxide is formed on the surface of a conventional replica mold (resin mold for nanoimprinting), and on this oxide film surface a release agent layer is further formed to not only enhance durability of the replica mold but also improve release properties.
However, in order to form an oxide layer on the surface of the resin layer as above, vacuum deposition technique of high level becomes necessary. Moreover, when a release agent layer is further formed on the surface of the oxide layer, a problem that the release agent layer is transferred from the replica mold also occurs.
In order to solve such problems, an invention of “a photo-curable resin composition characterized in that (a) one or more monomers having 3 or more acrylic groups and/or methacrylic groups in one molecule are contained in an amount of 20 to 60% by weight, (b) the amount of a component which is bonded by photo-curing reaction and becomes a solid is not less than 98% by weight, and (c) the viscosity at 25° C. is not more than 10 mPa·s” is disclosed in claim 1 of a patent literature 1 (Japanese Patent Laid-Open Publication No. 2009-19174), and in claim 3, it is described that this photo-curable resin composition contains 0.1 to 10% by weight of a silicone compound containing an acrylic group and/or a methacrylic group. Further, it is described in paragraph [0001] that the invention described in the cited literature 1 is an invention of a molded product produced by the use of this resin composition.
However, described in the cited literature 1 is an invention of improvement in mold release properties of the resin of the photo-curable composition by copolymerizing a silicone compound having an acrylic group or a methacrylic group. The silicon compound described in this cited literature 1 is a compound having reactive unsaturated groups such as acrylic groups or methacrylic groups at both ends, similarly to silicon diacrylate (see, for example, paragraph [0034] and paragraph [0035]). When a silicone compound having reactive unsaturated groups at both ends is used as above, the reactive unsaturated groups at both ends react with another monomer so as to form, for example, a crosslinked structure. Therefore, such a silicone compound is not present as a graft chain on the surface of the resin, and copolymerization of the silicon compound having reactive unsaturated groups at both ends rarely has influence on the mold release properties.
In claim 1 of a patent literature 2 (Japanese Patent Laid-Open Publication No. 2010-00612), an invention of “a curable composition for nanoimprinting, containing a monofunctional polymerizable compound in an amount of not less than 87% by mass and a poltopolymerization initiator” is described. In paragraph [0029], it is described that this curable composition for nanoimprinting preferably contains a silicone resin. However, described in this cited literature 2 is that mold release properties are imparted by adding the silicone resin, and such a silicone resin does not have reactivity with the resin that is a mainagent. By adding such a silicone resin alone, mold release properties are improved, but the silicone resin does not react with the resin that is a main agent, so that there is a problem that falling-off of the silicone resin is liable to occur.
In claim 1 of a patent literature 3 (Japanese Patent Laid-Open Publication No. 2006-198883), an invention of “a mold having a fine pattern on its surface and containing not less than 0.1% by mass of a fluorine-containing polymer containing recurring units based on at least one fluoromonomer selected from the group consisting of vinyl fluoride, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, pentafluoropropylene, hexafluoropropylene, fluoroacrylate and fluoromethacrylate” is disclosed.
In a patent literature 4 (Japanese Patent Laid-Open Publication No. 2006-182011), an invention of “a mold for photo-curable resin molding, having a fine pattern on its surface and having a total light transmittance of not less than 90% at wavelengths of 200 to 500 nm, wherein the mold contains not less than 50% by mass of a fluorine-containing polymer” is disclosed.
In the patent literatures 3 and 4, release properties are imparted to the resin mold by the use of a fluorine copolymer, and use of fluoroacrylate is also described. However, the fluoroacrylate used herein has a low molecular weight, and there is a problem that such graft chains as effectively act on the release properties are not formed.